Audiphone



R. E. POLK March 4, 1941.

AUDIPHONE Filed June //v l/EA/TOR R. E. POL K A T TORNE V Patented Mar. 4, 1941 UNITED STATES PATENT OFFICE AUDIPHONE Robert E. Polk, Brooklyn, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation oi New York Application June '30, 1938, Serial No. 216,692 3 Claims. I (01.179-107) operate a d capable of workingat high' gain without b oming unstable.

In order to keep the weigh-t of such devices low, it has been common practice to use a single battery unit for supplying current to both the f pick-up transmitter and the receiver networks.

Since the impedance of this battery is common units are used for the two networks, thereby avoiding the use of any elements of appreciable impedance in the common portion of the input and output circuits and making it possible to take full advantage of all the gain available. in the amplifier. As. each battery unit supplies only half the load, the units may be very small and the two units can be readily housed in a box no larger than that required for the single battery generally used.

The amplifier is housed in a casing which is mounted on the battery box by means of plugs engaging socket terminals in the batteries and connecting the batteries to the input and output circuits of the amplifier. A single. switch is used to control both circuits without producing appreciable coupling between them by mounting the switch within the amplifier casing so that the connections to the input and output circuits can be very short.

Mounting the switch in theamplifier casing also has the further advantage over other locations, such as in the transmitter or receiver cord, that these cords can be of the highly flexible two-conductor concentric type and can be identical and, therefore, interchangeable so that a single spare may be used in either position.

In the drawing, f

Fig. 1 shows an audiphone according to the invention;

Fig. 2 is a top view of the amplifier casing;

Figs. 3 and 4 are sectional views of the casing;

Fig. 5 is a detail view of the switch; and

Fig. 6 is a wiring diagram of the amplifier casing.

Referring to the drawing, the amplifier ll comprises essentially a small telephone receiver element l2 and. a transmitter element 13 having a I a knob 2| on the face of the transmitter.

common diaphragm which is normal to the plane of Fig. 3 of the drawing. This amplifier is preferably-of the type shown in the copending application of A. F. Bennett et al.. Serial No. 207,980, filed May 14, 1938. One end of the receiver winding and the diaphragm are electrically connected to the bracket 42 by means of which the amplifier is secured in position in the casing 14. The casing is provided with split metal plugs l5,

l5 and Hi, l6 which engage corresponding ter-' minal sockets in the battery units 11 and I8 in the battery box 19 and also serve as a means for mechanically holding the casing it in position on the box,as shown in Fig. 1.

While the efficiency of a properly designed amplifier does not vary a great deal with changes in its position, it is, of course, desirable that it be operated in the most efllcient position. Obviously, if the amplifier andbattery assembly is laid in such a position that the plane of the diaphragm is above the carbon of the transmitter element, the carbon may tend to fall away from the diaphragm" and reduce the efficiency. When the assembly is carried in the pocket of the user, the diaphragm is substantially vertical and when the assembly is placed on a desk or table, it will ordinarily be stood upright, as in Fig. l, or be laid fiat rather than on edge where it would be relatively unstable. The amplifier Ii is, therefore, mounted in the casing is in the position shown in Fig. 3 so that the diaphragm is vertical for all probable positions 01' use.

The pick-up transmitter 20' preferably has mounted in its casing a rheostat connected in series with the transmitter and operable to adjust the output to the desired level by means of The receiver 22 shown is of the bone conduction type with a head band 23 for holding it in position on the head of the user but, obviously, the re-' ceiver may be of any other suitable type. The transmitter and receiver are connected to terminal sockets 24, 25 and 26, 21 in the amplifier casing It by means of identical, two-conductor flexible cords 28 and 29 which are fitted at each end with plug type tips 30. Each of the terminal sockets 24 to 21 is' provided with a helical spring 3| which projects part way into the socket, as shown in Fig. 2, so that, when the cord tips are inserted into thesockets, the springs are deflected and maintain good electrical contact with the tips. I

When the switch 32 is operated from the position shown in Fig. 2 to the position of Fig. 5, the handle rotates about its axis 33 and forces the metal pin 34 upwardly into contact with all three of the spring members 35, 38 and 31. Current then fiows from the positive terminal oi battery I! over a circuit extending irom conductor 38, the springs 35 and 31 of the switch, conductor 39, the winding of the receiver element I! of the amplifier H, conductor Ill, cord 28, the pick up transmitter and rheostat and conductor 4| to the negative terminal of the battery.

The transmitter element I! of the amplifier and the receiver 22 are energized by battery unit it over a circuit extending from the positive terminal, conductor l3, springs 38 and 31 01' the switch, conductor 39, the transmitter element. l3, conductors ll and 29, the receiver unit 22, and conductor 15 to the negative terminal oi? the battery l8. In order to minimize the clicks due to switching, the springs 35 and 36 of the switch are preferably adjusted so that the transmitter circuit is made slightly before the receiver circuit is completed and is broken after the receiver circuit has been opened.

The general theory oi operation of audiphones is, of course, wellknown and requires no detailed discussion. It will be noted, however, that in this audiphone, since separate batteries are provided for the two networks, the current variations in the receiver circuit cannot react on the transmitter circuit. It, therefore, becomes practical to operate the amplifier at full gain at all times, to use simple cord circuits and to control the output volume at the pick-up trans mitter.

What is claimed is:

1. In an audiphone, a mechanical amplifier having input and output circuits, a pick-up transmitter in the input circuit, a receiver in the output circuit, separate batteries for the circuits, a casing for the amplifier and a switch in the casing controlling both of said circuits and having contacts so adjusted as to make the circuits in one sequence and break the circuits in the reverse sequence.

2. In an audiphone, a casing, a mechanical amplifier within the casing having input and output circuits including a short common conductor of low impedance, two terminals for each circuit for connecting the circuit to external batteries, two sockets for each circuit in the top of the casing for receiving transmitter and ceiver cords and a single switch mounted in the casing and connecting the common conductor to a battery terminal in each circuit to control both of said circuits.

3. In an audiphone, a pick-up transmitter, a receiver, a mechanical amplifier having a transmitter element, a receiver element and a dia-- phragm forming a mechanical coupling and a common electrical connection between the elements, circuits connecting the transmitter to the receiver elements and the transmitter element to the receiver, separate batteries Ior energizing said circuits, 8. switch connecting the common electrical connection to both batteries to control both circuits, a box for the batteries having one side substantially shorter than the other and means for mounting the switch and the amplifier on the battery box with the diaphragm of the amplifier parallel to the shorter side of the box.

' ROBERT E. POLI'I. 

